1. Field of the Invention
The present invention relates to a bismuth iron oxide powder and a manufacturing method for the bismuth iron oxide powder. In particular, the present invention relates to a nanograin bismuth iron oxide powder to be raw material of a dielectric ceramics and a manufacturing method for the nanograin bismuth iron oxide powder. The present invention also relates to a dielectric ceramics, and more particularly, to a dielectric ceramics containing BiFeO3 as a main component. The present invention also relates to a piezoelectric element using the dielectric ceramics, and a liquid discharge head and an ultrasonic motor which use the piezoelectric element.
2. Description of the Related Art
In the conventional electric and electronic industries, ceramics materials containing lead are widely used. A typical material thereof is Pb(Zr, Ti)O3 (hereinafter, referred to as “PZT”), or lead-containing relaxor materials such as Pb(Mg, Nb)O3. Each of them has a perovskite-type crystal structure, and lead (Pb) occupies the A-site of the crystal. The PZT ceramics has high piezoelectric performance, and hence the PZT ceramics is used as a piezoelectric element of an actuator or the like. In addition, a ceramics of the lead-containing relaxor material has a high dielectric constant and can be combined with a ferroelectric material such as PbTiO3 so as to obtain good temperature characteristics, therefore, the ceramics is used for an element such as a stack ceramics capacitor. The piezoelectric element and the capacitor use the dielectric ceramics, particularly the ferroelectric ceramics as a main component of the element, and the piezoelectric element and the capacitor are both classified to a dielectric element.
In this way, a ceramics containing lead can provide a high performance dielectric element. However, there is concern about bad influence to environment when the ceramics is produced and when it is scrapped. Therefore, it is requested to provide a dielectric ceramics having high performance without lead.
As a candidate of dielectric ceramics materials that do not contain lead, a material having a perovskite-type crystal structure whose the A-site is occupied by bismuth (Bi) is noted. The lead element has an outermost electron structure of 6s26p2, which becomes +2 valent if the A-site of the perovskite structure is occupied. Therefore, two of outermost electrons exist as a lone pair in lead ion at the A-site. The bismuth element has an outermost electron structure of 6s26p3, which becomes +3 valent if the A-site of the perovskite structure is occupied. Therefore, two of outermost electrons exist as a lone pair in bismuth ion of at A-site. In this way, the electron structure of the bismuth ion in the bismuth perovskite is similar to that of the lead ion in the lead perovskite, and hence similar characteristics can be expected. In particular, BiFeO3 and a solid solution and a compound using the same are considered to be a promising candidate for lead-free dielectric ceramics materials.
For instance, Japanese Patent Application Laid-Open No. 2007-287739 discloses Bi1-xLaxFeO3 as a piezoelectric material containing BiFeO3 as a main component. However, it is generally known that BiFeO3 and the material containing BiFeO3 as a main component have a large value of current (leakage current) when a voltage is applied, and hence BiFeO3 and the material containing BiFeO3 as a main component are not suitable as a dielectric material.
As one of methods of reducing a leakage current value of BiFeO3, Japanese Patent Application Laid-Open No. 2007-221066 discloses a method of substituting a part of Fe in a BiFeO3 film with manganese (Mn). Thus, a reduction of the leakage current value of the BiFeO3 film can be realized. However, there is no description about a reduction of the leakage current in a bulk BiFeO3 ceramics by adding Mn, and the effect in the bulk ceramics is not disclosed.